This small austere three-nave church is located in the lower part of the Cathedral and it is currently the oldest temple in Santander. A part of the floor is glazed in such a way that a site with ancient remains of Roman hot baths can be seen through. It is an austere church consisting of three naves separated by sturdy pillars and a three-apse altar end which shows the influence of monastic proto-Gothic art. The capitals are mainly decorated with vegetables, although some of them in the chapels and next to the Door of Pardon, which is related to pilgrimage, have a symbolic nature. The church was built in the Gothic style, despite the fact that its low height and the robustness of its supports give more a feeling of Romanesque seclusion. It houses a crucifix made of polychromatic stone, the relics of the Holy Martyrs and a Pietà carved in white stone by Gregorio Hernández.